1. Field of the Invention
The present invention pertains to the technical field of drawing or depicting graphic patterns by using a beam of electrically charged particles. More specifically, the invention is concerned with a circuit for processing errors which occurs upon division or conversion of graphic or pattern data such as data of a mask into a plurality of blocks each of a size susceptible to transfer onto a semiconductor wafer, for example, through irradiation with a beam of electrically charged particles.
2. Description of the Related Art
The electrically charged particle beam type pattern depicting apparatus of concern is an apparatus which is adapted to depitc a pattern such as a circuit pattern on a semiconductor wafer directly by irradiating it with a beam of electrically charged particles (also referred to as the electrically charged particle beam). Frequently, the amount or size of graphic or pattern data inputted to the electrically charged particle beam type pattern depicting apparatus is too large to be transferred onto to a wafer at one time. Accordingly, when a graphic pattern of a large size is to be depicted through irradiation with the electrically charged particle beam, the data for that pattern is divided into a plurality of pattern portions or blocks (hereinafter also referred to as subpatterns) each of a size suited for exposure of the wafer.
FIG. 3 of the accompanying drawings shows an input pattern data in the state divided into a plurality of blocks or subpatterns. In the figure, a reference numeral 21 denotes generally the input graphic pattern, and 22 denotes individual subpatterns resulting from division of the input pattern. The input pattern 21 is shown in solid lines, while the subpatterns are shown in broken lines. For division of the input pattern in such a manner as shown in FIG. 3, calculation therefor is performed up to a fractional value which is less significant than a value which is required for minimizing error making appearance on the boundary, whereon the numerical value resulting from the calculation is finally rounded on or off so that resolution as desired can be obtained.
More specifically, referring to FIGS. 4 and 5 of the accompanying drawings, let's consider, for example, division along a boundary between the adjacent subpatterns 23 and 24 shown in FIG. 3.
In FIG. 4, distance or gap between adjacent vertical lines X.sub.n (n=1, . . . ) represents a desired minimum resolution L.sub.0 of graphic data or pattern. When the coordinates and lengths of sides of the subpattern 23 resulting from the division contain errors smaller than the minimum resolution L.sub.0, mere rounding-up or -off of the values representing the coordinates and the lengths such that the data may conform to the necessary minimum resolution L.sub.0 will bring about gaps or overlaps between the adjacent subpatterns 23 and 24.
For convenience of explanation, only the X-coordinate data in the example illustrated in FIG. 4 will be considered. Let's represent the X-coordinate of a starting point of the subpattern 23 by X.sub.11, while representing error smaller than the minimun resolution L.sub.0 contained in the data of the X-coordinate X.sub.11 by L.sub.1, the length of a bottom side by L.sub.2, the X-coordinate of an end point of the subpattern by X.sub.12, the X-coordinate of a starting point of the subpattern 24 by X.sub.12, and represent by L.sub.3 the error contained in data of the X-coordinate X.sub.12 which error is smaller than the minimum resolution L.sub.0, respectively. Further, it is assumed that L.sub.1 &lt;L.sub.0 /2, L3.gtoreq.L.sub.0 /2 and that L.sub.3 -L.sub.1 &lt;L.sub.0.
On the conditions mentioned above, the rounding-up/off processing will result in that the error L.sub.1 of the X-coordinate X.sub.11 of the starting point of the subpattern 23 is rounded off, as a result of which the position of the starting point of the subpattern 23 is displaced to the coordinate X.sub.1, as shown at (c) in FIG. 4. Consequently, when the length of the bottom side of the subpattern 23 is considered, starting from the new coordinate X.sub.1, the X-coordinate X.sub.12 of the end point of that side is displaced by L.sub.1 to the coordinate X.sub.13 as shown at (c) in FIG. 4. The error in the length of the side given by (L.sub.3 -L.sub.1) is smaller than L.sub.0 /2 and thus rounded off. As a result, the end point X-coordinate X.sub.12 of the subpattern 23 is ultimately shifted to the coordinate X.sub.4, as can be seen in FIG. 4 at (d).
On the other hand, the X-coordinate X.sub.12 of the starting point of the subpattern 24 is rounded up because the error L.sub.3 has a value greater than L.sub.0 /2, inclusive thereof, and is thus displaced to the coordinate X.sub.5, as shown in FIG. 4 at (e). Consequently, there makes appearance a gap between the subpattern 23 and 24, as shown in FIG. 4 at (e) as well.
Now, it is assumed that L.sub.1 .gtoreq.L.sub.0 /2, L.sub.3 &lt;L.sub.0 /2 and that (L.sub.0 -L.sub.1)+L.sub.3 .gtoreq.L.sub.0 /2. In this case, the rounding-up/off processing results in that error L.sub.1 of the starting point X-coordinate of the subpattern 23 is rounded up to be displaced to the coordinate X.sub.2, as shown at (c) in FIG. 5. Accordingly, when the length of the bottom side is considered, starting from the new starting point X-coordinate X.sub.2, the X-coordinate X.sub.12 of the end point of the subpattern 23 is increased by (L.sub.0 -L.sub.1) to be displaced to the coordinate X.sub.13. Since the error in the length of the side given by (L.sub.3 +L.sub.0 -L.sub.1) is greater than L.sub.0 /2, inclusive thereof, the error is rounded up. Consequently, the end point X-coordinate X.sub.13 of the subpattern 23 is displaced to X.sub.5, as shown at (d) in FIG. 5. On the other hand, the X-coordinate X.sub.12 of the starting point of the pattern 24 is displaced to the X-coordinate X.sub.4, as shown at (e) in FIG. 5, because the error L.sub.3 is equal to L.sub.0 /2 and thus rounded up. As the ultimate result, there makes appearance overlap between the adjacent subpatterns 23 and 24, as shown in FIG. 5 at (e).
As will be understood from the above, the rounding-up/off processing results in that a gap equivalent to the minimum resolution L.sub.0 makes appearance between the adjacent subpatterns 23 and 24 in the case of the example illustrated in FIG. 4. On the other hand, in the case of the example shown in FIG. 5, an overlap corresponding to the minimum resolution L.sub.0 takes place between the subpatterns 23 and 24.
Needles to say, such gap and overlap which may make appearance upon division of the input graphic data, as described above, bring about concave portions or dents and convex portions or projections in the periphery of a pattern resulting from the depiction with the electrically charged particle beam, because the pattern is extremely fine, as exemplified by the fact that the pattern line is on the order of submicrons. Thus, there exists a great demand for eliminating the gap and/or overlap between adjacent subpatterns resulting from division of a graphic pattern to be imprinted.
Although the above description has been directed to the errors in the X-direction, it is self-explanatory that similar errors may occur in the Y-direction as well.